Hi I have two battery banks, start and house, house with victron monitor. Should I connect the negative cables of both battery banks together prior to the shunt or connect the unmonitored battery neg lead after the shunt. Thanks

Not sure whether I would call it before or after but connect the starting battery ground so current to the start battery does not pass through the shunt. You want the monitor to only measure the amps going in and out of the house batteries.

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Hi I have two battery banks, start and house, house with victron monitor. Should I connect the negative cables of both battery banks together prior to the shunt or connect the unmonitored battery neg lead after the shunt. Thanks

Connect the second "unmonitored" bank to the "load" side of the shunt not the "battery" side..

Not sure whether I would call it before or after but connect the starting battery ground so current to the start battery does not pass through the shunt. You want the monitor to only measure the amps going in and out of the house batteries.

If your bank features a parallel switch or combining relay the in-rush flows and equilibrium current flowing between banks when connected will throw off your monitors calculations just like a bilge pump that by-passes the shunt would. If the start battery is on the battery side of the shunt it should be moved..

If your second battery has the capability to be either a load or a charge source, via "combining banks", you should treat it as such. Either way you are NOT "monitoring" the second battery, just the bank the monitor is connected to, and you are only treating it as a load or charge source like any other load or charge source that could change the state of charge on the bank being monitored..

Connect the second "unmonitored" bank to the "load" side of the shunt not the "battery" side..

I do not think this is correct. If monitoring the house battery only (which is normal practice) the current in and out of the start battery should be ignored by the meter. To do this the start battery current should not be read by the meter and the start battery should be connected to the battery side of the shunt.
If the batteries are combined current will flow in, or out, of the house bank and this will be recorded by the shunt.

I do not think this is correct. If monitoring the house battery only (which is normal practice) the current in and out of the start battery should be ignored by the meter. To do this the start battery current should not be read by the meter and the start battery should be connected to the battery side of the shunt.
If the batteries are combined current will flow in, or out, of the house bank and this will be recorded by the shunt.

Yes, it is correct.. The monitor will not record anything going on with the start battery until you combine them. When you combine you need to know what left or came into the monotored bank or your accuracy will be compromised..
If you want an inaccurate monitor go ahead and connect your second bank to the batt side of the shunt..

Have i got a engine that is the ground and different from my house neg return and therefore this is why my Victron Energy BMV-602S is not seeing the battery being charged from the alternator IF so what do i need to do to make the BMV-602S work properly.....well monitor the ins and outs properly?